It has previously been disclosed in U.S. Pat. No. 3,207,742, to Van de Castle, that hexamethylphosphoramide (HMPA) can be used in combination with lithium hydrocarbon catalysts to produce polymers from 1,3-dienes having an increased 1,2-microstructure. However HMPA is a suspected carcinogenic and is therefore no longer desirable to be used in catalyst systems.
The present invention has developed a catalyst system employing substituted phosphoramide compounds for increasing 1,2-microstructure in polymers prepared from 1,3-dienes which are not suspected carcinogenic agents and reduce the rate of side reactions which occur during polymerization, thus adding stability to the polymerization reaction.